Switching on optical properties of D-π-A DSSC sensitizers from π-spacers towards machine learning

Abstract

Organic photovoltaic (OPV) solar cells recently achieved a reported efficiency as high as 17.3%. In this study we explore new avenues of shifting the light absorber through rational design of the π-spacers in the Donor–π-spacer–Acceptor dyes. That is, to construct high performing new dyes with fixed donor (DCPA) and acceptor (PMID) from appropriate π-building units of fluorene, EDOT and thiophene. These three π-units form various combinations of the π-conjugate spacers for new dyes. We focus on the development of the relationship between the three building units of π-spacers to construct new DCPA–π-spacer–PMID dyes and their UV–vis spectra in tetrahydrofuran (THF) solution. The latter (i.e., UV–vis spectra) are calculated using quantum mechanical time dependent density functional theory (TD-DFT) methods. This set of nine new organic dyes has been employed to develop augmented intelligence (AI). We discovered that repeating the fluorene (πO) unit alone in the π-spacer, such as OP100, OP200 and OP300 dyes, will lead to hyperchromic enhancement of the donor spectral band in the UV region of ca. 300 nm, with limited impact on the major spectral band at 500 nm which is stemmed from the acceptor (PMID). To maximize the UV–vis absorption, more efficient π-spacers for this class of dyes are constructed from mixtures of the fluorene (πO) and EDOT (πP) units, such as πO-πP-πO (OP210) or as πO-πP-πO-πP (OP220). The information obtained is useful to elucidate new dyes with desired properties with appropriate UV–vis spectra for future machine learning (ML).